The present invention. relates to a method and apparatus for ejecting material from a liquid. The invention employs technology the same as or similar to that described in WO97/27057, and, more particularly, it relates to the application of a differential voltage to the electrodes of a printhead.
In order to control the ejection of material the electrical potential gradient at an ejection location needs to be varied from below a threshold to above a threshold. This has been achieved by applying a voltage pulse to an ejection electrode. However, there are limitations in the availability of compact electronic drive circuits which are able to provide the required voltage pulses, and this presents particular problems in small printheads. Also, in printheads containing an array of ejection locations, capacitive coupling between proximate ejection locations can adversely effect ejection. This cross-talk can be reduced if lower voltages are used, and it is therefore desirable to use the smallest possible voltages to cause ejection.
EP-A-0 761 443 discloses an array printer having multiple ink outlets in which matrix addressing of the ink outlets is achieved by applying a voltage to individual ejection electrodes and an inverse voltage to common control electrodes in order to achieve ejection from specific ink outlets.
According to the present invention there is provided a method ejecting material from a liquid within a chamber of a multi-chamber ejection device having respective ejection and secondary electrodes associated with each chamber, the method comprising:
controlling the application of first voltage pulses to a respective ejection electrode associated with the chamber and second voltage pulses to a respective secondary electrode associated with the chamber, such that when a voltage pulse is applied to the ejection electrode a voltage pulse, inverted with respect to the pulse applied to the ejection electrode, is applied to the secondary electrode.
It should be understood that, in the context of this invention, the word xe2x80x9cinvertedxe2x80x9d is intended to define voltage pulses which may have either opposite signs, or voltage pulses with voltages that rise and fall in an opposing manner.
It should also be understood that, although there is no limitation to the pulses being of equal and opposite magnitude, it is preferable that the moduli of the change in voltage of the voltage pulses are equal.
According to the present invention there is also provided apparatus for ejecting material from a liquid, comprising
a plurality of chambers for containing the liquid; respective ejection and secondary electrodes associated with each chamber;
control means for applying first voltage pulses to a respective ejection electrode associated with a chamber and second voltage pulses to a respective secondary electrode associated with the chamber;
the control means controlling the first and second voltages such that, when a voltage pulse is applied to the ejection electrode, a voltage pulse, inverted with respect to the pulse applied to the ejection electrode, is applied to the secondary electrode.
Voltage pulses may be applied to multiple ejection electrodes and multiple secondary electrodes.